Does the BWM Convention permit exemptions to be granted from the ballast water management requirements?

Yes.

Under Regulation A-4 a flag State may grant exemptions in waters under its jurisdiction, but only to (1) ships on voyages between or operating exclusively between specified ports or locations; (2) for no more than five years subject to intermediate review; (3) provided the ships do not mix ballast water or sediments other than between these ports or locations; and (4) after risk assessment in accordance with IMO Guidelines.